Several different types of valve arrangements of the aforesaid kind are known to the art and used for various purposes.
For instance, U.S. Patent Publication 3,739,799 illustrates and describes a control system for mixing two gases and for use with anaesthetic apparatus. The control system includes a mixing control valve which is adapted to be able to vary continuously the relative proportions between two gaseous components without needing to alter the total rate of flow through the valve to this end.
Also shown is a control unit for varying the total rate of flow of these components without needing to alter the relative proportion therebetween.
More particularly, there is disclosed in this prior publication a valve arrangement which is adapted to mix at least two media and which includes a first inlet and a first valve means for a first medium, and a second inlet and a second valve means for a second medium, and an outlet for respective media or an outlet for a media mixture.
According to this publication, movement of the valve body of a first valve means away from and towards a first valve seat, and movement of the valve body of a second valve means away from and towards a second valve seat are mutually controlled so that an increase in the flow of the first medium through the first valve means will result in a corresponding reduction in the flow of the second medium through the second valve means, and vice versa.
It is also disclosed that the valve seats of respective valve means are positioned in a respective valve housings, whereas the first and the second valve bodies are formed in the end parts of a rod-like element that includes a screw thread which co-acts with a corresponding screw thread on a first valve housing such as to enable the rod-like element to be displaced axially backwards and forwards in response to the direction in which said element is rotated.
In the case of this known arrangement, a wheel protrudes partially through a slot provided in an operating panel and is turned from outside said panel.
A valve arrangement in which rotation of a wheel causes the valve body of a first valve means to move to a closed position and the valve body of a second valve means to move to an open position through the medium of a gearwheel arrangement is known from Swedish Patent Specification 330 749.
The German Patent Publication DE-A1-33 26 696 also discloses a valve arrangement in which two gases are mixed during a pressure difference balancing means and where the concentration of the mixture will be constant independently of pressure differences in the two gases.
This is caused by having a valve part attached to each of two diaphragms or membranes (7,8) and having valve seats (9,10) arranged between said membranes.
Each membrane is also supported by a spring arrangement (19,20) and the force caused by each of said spring arrangements is adjustable by a knob (21), the turning of which causes a higher or a smaller force.
This construction also includes two pressure chambers (15,16) one for each gas to be mixed. These pressure chambers are arranged between said membranes.